In the Combine many entities like facilities, ships, stations and vehicles are always owned by someone. The owner can set the entity to closed or open to all, and open to crewlist, or, in the case of a faction owned entity, open to faction.

In order to remove something from an entity, or to move the entity itself, you have to be inside it. In the case of ships, vehicles and raw materials (aka mats and RM's) you have to be assigned pilot or operator of the facility or entity.

Planets can also offer access issues if they are shielded, which will show up on descent as a blue overlay. The only way to see if you can get through the shield on descent is to try, on the second leg, atmo to ground. Shield access must generally be arranged.

Access is best requested a few hours before you actually need it to give time for it to actually be done.